Nucleation of twins by grain coalescence during the sintering of BaTiO 3 ceramics

Dedensification (up to 10% of the theoretical density inweakening of the electrical properties. 20 This has been previously demonstrated on hot-pressed BaTiO 3 samples during some instances) occurs at temperatures of .1320؇C during the sintering of commercial undoped BaTiO 3 powders. The annealing treatments. 21 The purpose of this paper is to clarify the principles of expansion of the rigid, interconnected network of large, rounded grains that grow by the Ostwald ripening effect dedensification processes during the sintering of undoped BaTiO 3 . The occurrence (or absence) of a dedensification step, as can explain the dedensification that is observed. The isotropic anomalous grain growth results from the appearance well as its magnitude and onset temperature, are discussed and correlated with anomalous grain growth, the grain-boundary of a liquid phase at }1320؇C and induces tensile stresses on the residual porous fine-grained matrix. No dedensification liquid phase, and the sintering pressure. A phenomenological was observed at temperatures of ,1320؇C, despite anisoexplanation involving expansion of the large grain skeleton will tropic anomalous grain growth.be proposed.

Section: Discussion (2) Isothermal Sintering (Dilatometer Furnace)mentioning

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Dedensification and Anomalous Grain Growth during Sintering of Undoped Barium Titanate

Demartin

Hérard

Carry

et al. 1997

“…However, their ␥-plot must vary with the x value. According to previous investigations, the equilibrium shape of a BaTiO 3 single crystal consists of {100} and {111} planes, 22,23 whereas that of a SrTiO 3 single crystal consists of {100} and {110}. 24,25 This result suggests that the stability of {111} planes relative to {110} planes decreases as the concentration of strontium in (Ba,Sr)TiO 3 increases.…”

Section: (2) Formation Of {111} Twins and Abnormal Grain Growth In Bamentioning

confidence: 74%

{111} Twin Formation and Abnormal Grain Growth in Barium Strontium Titanate

Lee

Jung

Kang

et al. 2003

Two series of experiments were performed to study the experimental conditions for the formation of {111} twins and related microstructures in barium strontium titanate ((Ba, Sr)TiO3). In the first series, the phase equilibria in the BaTiO3–SrTiO3–TiO2 system were determined. XRD and WDS analysis, done in the BaTiO3‐rich region, of 45(Ba,Sr)TiO3–10TiO2 samples annealed at 1250°C for 200 h in air showed that (Ba,Sr)TiO3 was in equilibrium with Ba6Ti17O40 (B6T17) and Ba4Ti13O30 phases with strontium solubility (Sr/(Ba + Sr)) of ∼0.02 and 0.20, respectively. In the second series the microstructures of samples consisting of a mixture of (Ba,Sr)TiO3 and 2.0 mol% TiO2, were observed after sintering at 1250°C for 100 h in air. {111} twins formed only in the samples with faceted B6T17 second phase particles, similar to the case of BaTiO3. In these samples, abnormal grain growth occurred in the presence of the {111} twins. In contrast, no {111} twins formed and no abnormal grain growth occurred in the samples containing second phase particles other than B6T17. With an increased substitution of strontium for barium, the aspect ratio of abnormal grains containing {111} twin lamellae was reduced. This result was attributed to a reduction in the relative stability of the {111} planes with the strontium substitution.

“…Coalescence of facetted grains in systems with an incompletely wetting liquid to form twinned grains or grains with low-angle boundaries has also been proposed, 21,22 particularly for BaTiO 3 . Calculations of the likelihood of forming single and double twins based on geometric probabilities of twin formation seem plausible, depending on the angular acceptance criteria chosen.…”

Section: Resultsmentioning

confidence: 99%

Grain Growth and Twin Formation in 0.74PMN·0.26PT

Wallace

Huh

Blendell

et al. 2002

The mechanisms controlling normal and exaggerated grain growth in lead magnesium niobate-lead titanate (PMN-PT) ceramics have been investigated by varying the PbO-based liquid-phase volume fraction from 0.03 to 0.6 and sintering temperature from 900°to 1100°C. There is a transition in matrix grain growth rate and matrix grain shape with liquid fraction; samples with liquid volume fractions less than ϳ0.15 show relatively small equiaxed grains resulting from grain-tograin impingement. Samples with higher liquid fractions show significantly larger, facetted, cube-shaped grains, whose size is independent of liquid fraction, indicating that a surface nucleation rate mechanism controls growth in this regime. Exaggerated grains were found in the high liquid fraction samples. Electron backscatter diffraction showed that all of the exaggerated grains contained 60°͗111͘ twins but none of the normal matrix grains contained twins. The reentrant angles in the twinned grains give them a growth advantage over untwinned grains, resulting in a population of exaggerated grains.